1. Field of the Invention
The present invention relates to a composition which forms a highly scratch-resistant and transparent coating having a high refractive index on a surface of a transparent solid material, and in particular, it relates to a transparent coating composition for use on a plastic lens.
2. Related Art
A plastic material is utilized as a transparent solid substitute for glass due to its light weight and excellent processability. Since, however, the plastic material is softer than glass, it is easily scratched. It is therefore known to form a transparent coating layer on a surface of a transparent solid material such as a transparent plastic material, or the like, in order to protect the surface of said transparent solid material and impart the surface with wear resistance. For example, Japanese Patent Publication No. 37142/1988 discloses a method of coating on a transparent solid material with a metal oxide such as antimony oxide, or the like and an organosilicon polymer, and Japanese Patent Publication No. 56093/1989 discloses a method of coating a transparent solid material with antimony oxide or aluminum acetate and a partial condensate of organosilicon.
Japanese Patent Publication Tokkai No. 80359/1983 discloses a coating composition for use on a transparent solid material, which is obtained by adding alkyl, a vinyl or phenylsilanol partial condensate, a partial condensate of epoxy-based silanol and a crosslinking agent selected from polyfunctional carboxylic acid, a polyfunctional carboxylic acid anhydride and polyfunctional imide to colloidal silica.
Further, Japanese Patent Publication Tokkai No. 306477/1989 discloses a coating composition for use on a transparent solid material, which comprises antimony oxide, alumina sol, titania sol, etc., and epoxy group-containing silane, etc.
When the coating composition disclosed in any of the above prior art is coated on a transparent glass or plastic material having a high refractive index, interference fringes are observed due to a slight nonuniformity in the thickness of the coating layer when light is reflected, since the refractive index of the coating layer is relatively low. In particular, when the above transparent solid material is a lens for spectacles, the lens appearance is impaired and such a lens has no commercial value.
The coating layers obtained by the above prior art cannot be said to be excellent in dyeing properties. When a transparent solid material having such a coating layer is applied to sunglasses or window glass, therefore, there have been cases where the coating layer cannot be dyed with a conventional dye.